1. Field of the Invention
This invention relates to roadway markers or guide posts. More particularly, it is concerned with resilient posts which permit nondestructive deformation upon impact by a moving object.
2. Prior Art
Vehicle traffic control requires the use of road signs and markers as aids in solving the various problems associated with traffic safety and direction. It has been found that a useful characteristic for such signs and markers is that these posts have the ability to withstand vehicle impact, without requiring subsequent replacement. An attempt has been made to fill this need with various configurations of posts. However, the structural design of such posts has involved the consideration of two opposing structural features, i.e. the elasticity required during dynamic conditions to permit the post to nondestructively bend with vehicle impact and the longitudinal rigidity required during static conditions to withstand forces resulting as the post is driven into a hard surface.
The elasticity is necessary in view of frequent high speeds associated with impacts between a moving vehicle and stationary post. In such cases, if the post could not bend it would likely shear off, and would have to be replaced. Mere bendability, however, is not sufficient, since each time a post was bent it would have to be straightened before it could again be functional. This could involve high maintenance costs. Ideally, a post should also have sufficient elasticity that it will automatically assume its proper upright configuration after dissipation of any impact forces.
While elasticity is desirable, the elasticity may present a practical problem when installation of the post is considered. In the past, when deformable plastics have been used as post material, installation has frequently required predrilling a hole or insertion of some support receptacle into the ground, with the subsequent positioning of the plastic post into the hole or receptacle. These preliminary steps were required because such previously known elastic posts would not withstand a buckling force applied during attempts to drive the posts into hard surfaces. Consequently, the same elastic properties which permitted the nondestructive deformation upon impact caused the buckling of a post subjected to a driving force along its axis.
Attempts have been made to incorporate the dual requirements of elasticity and rigidity by utilizing a spring within an otherwise rigid post, and with the rigid parts of the post being secured on opposite ends of the spring. Installation was by compressing the spring and then pounding along the now rigid longitudinal axis. After installation, the deformable character of the post was accomplished by the transverse elastic property of the included spring.
This configuration, however, has several apparent disadvantages. The rigid portion of the structure has customarily been made of strong materials which may dent or otherwise damage the impacting vehicle. Furthermore, the use of such rigid materials and springs and the assembly requirements result in excessive costs for the posts.
U.S. Pat. No. 3,875,720 discloses a second approach to the problem, of providing elasticity in a post that can be driven. In this patent a post is formed by a bundle of flexible rods that are clamped together to obtain the desired rigid property required during the static installation stage of the post. Deformation of the post during dynamic conditions is permitted by deflection of the various flexible rods away from the central axis of the post structure. Here again, however, economic factors appear to have impeded utilization of such structure despite the growing need for such a post.